Plastic materials are easy to form, can be easily formed into a variety of shapes and have, therefore, been widely used in a variety of applications. Specifically, directly blow-formed bottles of which the inner wall surfaces are formed by using an olefin resin such as low-density polyethylene, have been widely used as containers for containing viscous fluid substances such as ketchup, mayonnaise and the like by utilizing their squeezing properties or squeeze-out properties.
Here, the containers for containing viscous fluid substances must have an inner surface that exhibits highly slipping property for the contents such that the contents can be discharged quickly and completely up to the last drop without remaining in the containers.
So far, the slipping property has been attained by blending a resin that forms the inner surface of the container with an additive such as lubricant. In recent years, however, there have been proposed various kinds of technical arts for improving surface properties such as slipping properties to viscous substances by forming a liquid film on the surface of a resin base material (e.g., see patent documents 1, 2 and 3).
According to the above technical arts, the slipping property can be strikingly improved as compared to the case of adding an additive such as lubricant to the resin that forms the surface of the base material, and attention has now been paid thereto.
Here, according to means for improving surface properties by forming the liquid film on the surface, it becomes necessary to stably hold the liquid film on the surface. To do so, the above patent documents 1 to 3 are all forming fine ruggedness in the surfaces.
Here, though the ruggedness is formed in the surfaces in an attempt to stably maintain the liquid film, no relation has yet been closely studied between the degree of ruggedness and the slipping property of the fluid substance moving on the liquid film.